Circuit interrupter with digital trip unit and power supply

ABSTRACT

A circuit breaker includes a microprocessor-based trip unit and a power supply for supplying operating power to the trip unit and the trip coil of the circuit breaker from either the internal current transformers of the circuit breaker or a plurality of external sources. The trip unit includes a numeric display for displaying a sequential series of parameter values under normal conditions. Under low-power conditions, the power supply provides pulses of operating power sufficient to enable the trip unit to execute all of its limit check functions and present a flashing display of a single parameter value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to material disclosed in the followingcopending U.S. patent applications, all of which are assigned to thesame assignee of the present application.

Ser. No. 140,559, "Circuit Interrupter With Solid State Digital TripUnit" filed Apr. 15, 1980 by J. C. Engel;

Ser. No. 140,631, "Circuit Interrupter With Front Panel Numeric Display"filed Apr. 15, 1980 by J. C. Engel, R. T. Elms, and G. F. Saletta;

Ser. No. 140,632, "Circuit Interrupter With Solid State Digital TripUnit And Positive Power-Up Feature" filed Apr. 15, 1980 by R. T. Elms,G. F. Saletta, and B. J. Mercier;

Ser. No. 140,627, "Circuit Interrupter With Digital Trip Unit AndOptically-Coupled Data Input/Output System" filed Apr. 15, 1980 by J. C.Engel, J. A. Wafer, J. T. Wilson, and R. T. Elms;

Ser. No. 140,554, "Circuit Interrupter With Energy Management Functions"filed Apr. 15, 1980 by J. T. Wilson, J. A. Wafer, and J. C. Engel;

Ser. No. 140,628, "Circuit Interrupter With Digital Trrip Unit And StyleDesignator Circuit" filed Apr. 15, 1980 by J. J. Matsko, E. W. Lange, J.C. Engel, and B. J. Mercier;

Ser. No. 140,504, "Circuit Interrupter With Overtemperature Trip Device"filed Apr. 15, 1980 by J. J. Matsko, and J. A. Wafer;

Ser. No. 140,553, "Circuit Interrupter With Digital Trip Unit And MeansTo Enter Trip Settings" filed Apr. 15, 1980 by R. T. Elms, J. C. Engel,B. J. Mercier, G. F. Saletta, and J. T. Wilson;

Ser. No. 140,557, "Circuit Interrupter With Multiple Display AndParameter Entry Means" filed Apr. 15, 1980 by J. J. Matsko, J. A. Wafer,J. C. Engel, and B. J. Mercier;

Ser. No. 140,556, "Circuit Interrupter With Remote Indicator And PowerSupply" filed Apr. 15, 1980 by J. C. Engel, J. A. Wafer, B. J. Mercier,and J. J. Matsko;

Ser. No. 140,625, "Circuit Interrupter With Digital Trip Unit AndAutomatic Reset" filed Apr. 15, 1980 by B. J. Mercier and J. C. Engel;and

Ser. No. 140,558, "Circuit Interrupter With Digital Trip Unit AndPotentiometers For Parameter Entry" filed Apr. 15, 1980 by J. C. Engel,B. J. Mercier, and R. T. Elms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to circuit interrupters having means forelectronically analyzing the electrical conditions on the circuit beingprotected and for automatically opening to interrupt the current flowwhenever electrical conditions exceed predetermined limits.

2. Description of the Prior Art

Circuit breakers are widely used in industrial and commercialapplications for protecting electrical conductors and apparatusconnected thereto from damage due to excessive current flow. Althoughinitially used as direct replacements for fuses, circuit breakers weregradually called upon to provide more sophisticated types of protectionother than merely interrupting the circuit when the current flowexceeded a certain level. More elaborate time-current tripcharacteristics were required such that a circuit breaker would rapidlyopen upon very high overload conditions but would delay interruptionupon detection of lower overload currents, the delay time being roughlyinversely proportional to the degree of overload. Additionally, circuitbreakers were called upon to interrupt upon the detection of groundfault currents. As the complexity of electrical distribution circuitsincreased, the control portions of circuit breakers were interconnectedto provide selectivity and coordination. This allowed the designer tospecify the order in which the various circuit breakers would interruptunder specified fault conditions.

During the late 1960's, solid state electronic control circuits weredeveloped for use in high power low voltage circuit breakers. Thesecontrol circuits performed functions such as instantaneous and delayedtripping which were traditionally achieved by magnetic and thermalmeans. The improved accuracy and flexibility of the solid stateelectronic controls resulted in their wide-spread acceptance, eventhough the electronic control circuits were more expensive than theirmechanical counterparts.

The earliest electronic control circuit designs utilized discretecomponents such as transistors, resistors, and capacitors. More recentdesigns have included integrated circuits which have provided improvedproduct performance at a slightly reduced cost.

As the cost of energy continues its rapid rise, there is increasinginterest in effectively controlling the usage of electrical energythrough the design of more sophisticated electrical distributioncircuits. Therefore, there is required a circuit breaker providing amore complex analysis of electrical conditions on the circuit beingprotected and even greater capability for coordination with otherbreakers. As always, it is extremely desirable to provide thiscapability at the same or lower cost.

In providing basic overcurrent protection functions, it would bedesirable to provide a circuit interrupter requiring no connectionsother than line connections to the circuit being protected. Therefore,it is desirable to provide a circuit interrupter having a trip unitpowered by the circuit being protected while at the same time providingrequired isolation. For additional functions, however, such as displayof the value of current which caused a trip and various energyfunctions, it is desirable that the trip unit be powered independentlyfrom the circuit being protected. Accordingly, it is desired to providea circuit interrupter having the capability of being powered from avariety of power sources and including means for selecting the mostappropriate power source at any given time. In addition, underconditions of inadequate power availability, it is desired that thecircuit breaker provide the maximum functions possible for the level ofpower available.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, there isprovided circuit interrupter apparatus including interrupter means foroperating to interrupt current flow through an associated circuit oncommand, sensing means for sensing current flow through the interruptermeans, and trip unit means connected to the interrupter means and thesensing means for comparing current flow through the interrupter meansto a predetermined time-current trip characteristic and for operatingthe interrupter means whenever current flow therethrough exceeds thetime-current trip characteristic. The apparatus also includes powersupply means connected to the sensing means and to a source of externalpower for supplying operating power to the trip unit, the power supplymeans selecting the most appropriate power source as between the sensingmeans and the external power source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a circuit breaker embodying theprinciples of the present invention;

FIG. 2 is a functional block diagram of the circuit breaker of FIG. 1;

FIG. 3 is a block diagram of a typical electrical distribution systemutilizing circuit breakers of the type shown in FIG. 1;

FIG. 4 is a graph of the time-current tripping characteristic of thecircuit breaker shown in FIG. 1, plotted on a log-log scale;

FIG. 5 is a detailed frontal view of the trip unit panel of the circuitbreaker of FIGS. 1 and 2;

FIG. 5A is a block diagram of the microcomputer shown in FIG. 2;

FIG. 6 is a detailed schematic diagram of the panel display system ofFIG. 5; and

FIG. 7 is a detailed schematic diagram of the parameter input system ofFIG. 2;

FIG. 8 is a detailed schematic diagram of the Style Number DesignatorSystem of FIG. 2;

FIG. 9 is a schematic diagram of the Remote Indicator and Power Supplyof FIG. 2;

FIG. 10 is a diagram of the waveforms present at various locations inthe Remote Indicator and Power Supply of FIG. 9;

FIG. 11 is a block diagram of the System Power Supply shown in FIG. 2;

FIG. 12 is a schematic diagram of the System Power Supply shown in FIG.11;

FIG. 13 is a diagram of the switching levels occuring at variouslocations in the System Power Supply of FIGS. 11 and 12;

FIG. 14 is a schematic diagram of the Data Input Output System and PowerSupply of FIG. 2;

FIG. 15 is a diagram of the waveforms present at various locations inthe system of FIG. 14;

FIG. 16 is a schematic diagram of a power-on hardware initialization andautomatic reset circuit;

FIG. 17 is a flowchart of the main instruction loop stored in read-onlymemory of the microcomputer shown in FIG. 2;

FIG. 18 is a flowchart of the first function of the main instructionloop shown in FIG. 17;

FIG. 19 is a flowchart of the second function of the main instructionloop shown in FIG. 17;

FIG. 20 is a flowchart of the third function of the main instructionloop shown in FIG. 17;

FIG. 21 is a flowchart of the fourth function of the main instructionloop shown in FIG. 17;

FIG. 22 is a flowchart of the fifth function of the main instructionloop shown in FIG. 17;

FIG. 23 is a flowchart of the sixth function of the main instructionloop shown in FIG. 17;

FIG. 24 is a flowchart of the seventh function of the main instructionloop shown in FIG. 17;

FIG. 25 is a flowchart of the eighth function of the main instructionloop shown in FIG. 17;

FIG. 26 is a flowchart of the common display subroutine of FIG. 17;

FIG. 27 is a flowchart of the trip subroutine of FIG. 17; and

FIG. 28 is a flowchart of the subroutine to obtain setting values fromthe potentiometers of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT I. INTRODUCTION

A. Use of a Circuit Breaker in an Electrical Power Distribution System

Before explaining the operation of the present invention, it will behelpful to describe in greater detail the function of a circuit breakerin an electrical power distribution circuit. FIG. 3 shows a typicalelectrical distribution system. A plurality of electrical loads 48 aresupplied through circuit breakers 50, 52 and 54 from either of twosources of electrical energy 56 and 58. The sources 56 and 58 could betransformers connected to a high voltage electrical feeder line, adiesel-powered emergency generator, or a combination of the two. Powerfrom the first source 56 is supplied through a first main circuitbreaker 50 to a plurality of branch circuit breakers 60-66. Similarly,power from the second source 58 may be supplied through a second maincircuit breaker 52 to a second plurality of branch circuit breakers68-74. Alternatively, power from either source 56 or 58 may be suppliedthrough the tie circuit breaker 54 to the branch circuit breakers on theopposite side. Generally, the main and tie circuit breakers 50, 52 and54 are coordinated so that no branch circuit is simultaneously suppliedby both sources. The capacity of the main and tie circuit breakers 50,52 and 54 is usually greater than that of any branch circuit breaker.

If a fault (abnormally large current flow) should occur at, for example,the point 76, it is desirable that this condition be detected by thebranch circuit breaker 62 and that this breaker rapidly trip, or open,to isolate the fault from any source of electrical power. The fault atthe point 76 may be a large over-current condition caused, for example,by a short circuit between two of the phase conductors of the circuit,or an overload only slightly above the rating of the breaker caused by astalled motor. Alternatively, it might be a ground fault caused by abreakdown of insulation on one of the conductors, allowing a relativelysmall amount of current flow to an object at ground potential. In anycase, the fault would also be detected by the main or tie breakers 50,52 or 54 through which the load fed by branch breaker 62 is supplied atthe time of the fault. However, it is desirable that only the branchcircuit breaker 62 operate to isolate the fault from the source ofelectrical power rather than the main or tie breakers. The reason forthis is that if the main or tie circuit breaker should trip, electricalpower would be lost to more than just the load attached in the branchcircuit on which the fault occurred. It is therefore desirable that themain and tie circuit 50, 52 and 54 breakers should have a longer delayperiod following direction of a fault before they initiate a trippingoperation. The coordination of delay times among the main, tie andbranch circuit breakers for various types of faults is a major reasonfor the need to provide sophisticated control in a trip unit.

B. Time-Current Tripping Characteristics

In order to achieve the coordination between circuit breakers asdescribed above, the time vs. current tripping characteristics of eachcircuit breaker must be specified. Circuit breakers have traditionallyexhibited characteristics similar to that shown in FIG. 4, where bothaxes are plotted on a logarithmic scale. When current below the maximumcontinuous current rating of the breaker is flowing, the breaker will,of course, remain closed. As current increases, however, it is desirablethat at some point, for example the point 300 of FIG. 4, the breakershould trip if this overload current persists for an extended period oftime. Should a current flow equal to the maximum continuous currentrating as specified by point 300 persist, it can be seen from FIG. 4that the breaker will trip in approximately 60 seconds.

At slightly higher values of current, the time required for the breakerto trip will be shorter. For example at 1.6 times maximum continuouscurrent as specified by point 302, the breaker will trip in about 20seconds. The portion of the curve between the points 300 and 304 isknown as the long delay, or thermal, characteristic of the breaker,since this characteristic was provided by a bimetal element intraditional breakers. It is desirable that both the current level atwhich the long delay portion begins and the trip time required for anypoint on that portion be adjustable. These parameters are known as longdelay pick-up and long delay time, respectively, and are indicated bythe arrows 306 and 309.

At very high overcurrent levels, for example 12 times the maximumcontinuous current and above, it is desirable that the circuit breakertrip as rapidly as possible. This point 312 on the curve is known as the"instantaneous", or magnetic, trip level since traditional breakersemployed an electromagnet in series with the contacts to provide themost rapid response. The instantaneous pick-up level is usuallyadjustable, as indicated by the arrow 314.

To aid in coordinating breakers within a distribution system, moderncircuit breakers have added a short delay trip characteristic 316between the long delay and instantaneous portions. The present inventionallows adjustment of both the short delay pick-up level and the shortdelay trip time as indicated by the arrows 318 and 320.

Under certain conditions it is desirable that the trip time over theshort delay portion also vary inversely with the square of the current.This is known as an I² t characteristic and is indicated in FIG. 4 bythe broken line 310.

II. PHYSICAL AND OPERATIONAL DESCRIPTION

A. Circuit Breaker

Reference may now be had to the drawings, in which like referencecharacters refer to corresponding components. A perspective view and afunctional block diagram of a molded case circuit breaker 10 employingthe principles of the present invention is shown in FIGS. 1 and 2,respectively. Although the circuit interrupter 10 is a three-polecircuit breaker for use on a three-phase electrical circuit, theinvention is, of course, not so limited and could be used on asingle-phase circuit or another type of multiphase circuit. A powersource such as a transformer or switchboard bus is connected to inputterminals 12 and an electrical load is connected to output terminals 14.Internal connected 16 conducted to the terminals 12 and 14 are alsoconnected to interrupting contacts 18 which serve to selectively openand close an electrical circuit through the circuit breaker. Thecontacts 18 are mechanically operated by a mechanism 20 which respondsto manually or automatically-initiated commands to open or close thecontacts 18.

Current transformers 24 surround each of the internal phase conductors16 to detect the level of current flow through the conductors 16. Theoutput signal from the current transformers 24 is supplied to a tripunit 26, along with the output signal from a current transformer 28which detects the level of ground fault current flowing in the circuit.The trip unit 26 constantly monitors the level of phase and ground faultcurrents flowing in the circuit to which the breaker 10 is connected andinitiates a command signal to a trip coil 22 which actuates themechanism 20 to open the contacts 18 whenever electrical conditions onthe circuit being protected exceed predetermined limits stored in thetrip unit 26. During normal conditions, the mechanism 20 can becommanded to open and close the contacts 18 through manually-initiatedcommands applied through the manual controls 32.

Referring to FIG. 1, it can be seen that the circuit breaker 10 includesa molded insulating housing 34. The terminals 12 and 14 are on the rearof the housing 34 and are thus not shown in FIG. 1. A handle 36 ismounted on the right-hand side of the housing 34 to allow an operator tomanually charge a spring (not shown) in the mechanism 20. The manualcontrols 32 are positioned in the center of the housing 34. Windows 38and 40 indicate the state of charge of the spring and the position ofthe contacts 18, respectively. A push-button 42 allows an operator tocause an internal electric motor to mechanically charge the spring inthe same manner as the manual charging operation which can be performedby the handle 36. A pushbutton 44 allows an operator to cause the springto operate the mechanism 20 to close the contacts 18. Similarly, apushbutton 46 allows an operator to cause the spring and mechanism 20 toopen the contacts 18.

B. Trip Unit

1. Front Panel

The panel of the trip unit 26 is positioned on the left side of thehousing 34 as can be seen in FIG. 1. This panel, shown in more detail inFIG. 5, includes a plurality of indicator lights, potentiometers,numeric display devices, and switches, to permit an operator to observethe electrical parameters on the circuit being protected and the limitvalues presently stored in the trip unit, and to enter new limit valuesif so desired.

A rating plug 78 is inserted into the front panel of the trip unit 26 tospecify the maximum continuous current to be allowed in the circuitbeing protected by the circuit breaker. This may be less than the actualcapacity of the circuit breaker, which is known as the frame size. Forexample, the frame size for the circuit breaker may be 1,600 amperes;however, when the breaker is initially installed the circuit beingprotected may need to supply only 1,000 amperes of electrical current.Therefore, a rating plug may be inserted in the trip unit to ensure thatthe maximum continuous current allowed by the circuit breaker will beonly 1,000 amperes even though the circuit breaker itself is capable ofsafely carrying 1,600 amperes.

An auxiliary AC power receptacle 132 is located at the upper right ofthe trip unit panel, as seen in FIG. 5. This socket is used to supplyauxiliary alternating current operating power (separate from theelectrical circuit being protected) to the circuitry of the trip unit.The operation of this auxiliary AC power supply will be described morecompletely in section III.E.

2. Block Diagram

Referring to FIG. 2, it can be seen that the trip coil 22 is suppliedwith power through a conductor 136 from the power supply 144. The flowof current through the trip coil is controlled by a non-latchingswitching device such as a switching field effect transistor 192actuated by the main trip unit circuitry. The use of a non-latchingswitch device instead of an SCR or other type of latching device as usedin the prior art provides greater noise immunity.

In addition, the circuit breaker 10 includes three parallel-connectednormally-open thermally activated switches 141 connected in parallelwith FET 192. These switches are physically mounted on the conductors 16in proximity to the contacts 18, with one switch mounted on each phaseconductor 16.

Each switch 141 comprises a bimetal element which closes the switchcontacts when the temperature of the associated conductor rises to 150°C. and resets when the conductor temperature falls below 130° C.Although a bimetallic switch is employed in the disclosed embodiment,other types of thermally activated switches such as thermistors could bemounted on the conductor. Alternatively, radiation sensors could beused. Infrared detectors could monitor the heat generated on thecontacts or conductors, while ultraviolet or RF detectors could senseradiation generated by arcing contacts or terminals.

The switches 141 serve to directly energize the trip coil 22 upon hightemperature conditions. In addition, the hardware interrupt line INT ofthe microcomputer is connected through the trip coil 22 to the high sideof the switches 141 to signal the microcomputer 154 that a tripoperation has occurred. This causes execution of appropriateinstructions in internal read-only memory (ROM) of microcomputer 154 togenerate output data to a remote indicator 145. Since the mechanism 20requires somewhat more than 30 ms. to open the contacts following a tripcommand, power is available for trip unit 26 to execute 2 completeoperation cycles of the main loop program even if no external power issupplied. Alternatively, the switches 141 could be wired solely to themicrocomputer 154 to allow it to initiate the trip operation andgenerate output data in the same manner as an overcurrent trip.

Information concerning electrical parameters on the circuit is providedby the three phase current transformers 24, each of which monitorscurrent flow through the individual phase conductors of the circuit. Thetransformer 28 surrounds the three phase conductors of the circuit anddetects currents which flow outward from a source through the phaseconductors and then return through unauthorized paths through ground,commonly known as ground fault currents.

The signals from the current transformers 24 are supplied to a rectifierand auctioneering circuit 142 which provides a DC current proportionalto the highest instantaneous AC current on any of the three phases. Thecircuit 142 provides normal operating power for the trip unit through apower supply 144. The transformers 24 and 28 act as current sources andare limited to supply power to the circuit 142 at approximately 40volts. This is converted by the power supply 144 to three operatingvoltages: a 1.67 volt reference voltage labeled V_(REF), a 5 voltoperating voltage for the microcomputer and associated circuitry of thetrip unit, and a 40 volt supply which operates the trip coil 22.Information from the rectifier and auctioneering circuit 142 which isproportional to the present value of phase current is also supplied tothe peak detector 160 of the main trip unit circuitry as indicated inFIG. 2.

The signal from the ground transformer 28 is supplied to a rectifiercircuit 146 which provides an alternate source of operating power forthe trip unit through the power supply 144, and also suppliesinformation proportional to the present value of ground current to thepeak detector 162 of the trip unit circuitry. An external DC source 148of operating power on the order of about 40 volts may also be suppliedto the power supply 144, as may be an external AC source 150 ofoperating power supplied through the trip unit front panel socket 132 toa rectifier 152 and then to the power supply 144.

The main trip unit circuitry includes an information processor andsequence controller 154 which may be, for example, a type 8048microcomputer obtainable in commercial quantities from the IntelCorporation. A block diagram of the controller 154 is shown in FIG. 5A;however, a detailed description of the 8048 microcomputer may beobtained from the MCS-48 Microcomputer User's Manual, published by theIntel Corporation.

An analog-to-digital converter 156 such as the type ADC3084 obtainablein commercial quantities from the National Semiconductor Corporation isconnected to the data bus 172 of the microcomputer 154. Any of eightinputs to the analog-to-digital converter (ADC) 156 are selected througha multiplexer 158 such as the type CD4051B according to an addresssupplied by the microcomputer via port 1 to the multiplexer 158. Theseinputs include peak detectors 160 and 162 for phase and ground currentvalues, an averaging circuit 164 for average phase current, a pair ofmultiplexers 166 and 168 for reading panel switches and potentiometersaddressed and selected by the microcomputer via port 2, and four linesfrom a style number designator circuit 170. The designator circuit 170allows manufacturing personnel to provide the microcomputer 154 withinformation concerning the optional features and modes, such as groundfault detection and serial I/O capability, with which the specific tripunit will be supplied. Use of such a designator circuit allows a singlemicrocomputer configuration to be provided for a plurality of differentmodels of the trip unit 26.

Also connected to the microcomputer data bus 172 is an externalread-only memory (ROM) 151 and a data input/output system 174 whichallows the trip unit to interact with other components and circuitbreakers of the electrical distribution system. Power for the datainput/output system is provided by a separate power supply 176 derivedfrom the five-volt bus of the power supply 144. As will be morecompletely described in a later section, the data input/output powersupply 176 is a pulse-type power supply activated by a line 178connected to port 1 of the microcomputer 154.

Input to the microcomputer 154 from the limit value potentiometers andswitches of the trip unit panel, shown in FIG. 2, is supplied throughmultiplexers 166 and 168 to multiplexer 158. Output information to thepanel display system 155 including the LED's 84-100 and numeric displayindicators 80 and 82 is supplied from the microprocessor 154 throughport 2. Port 2 also supplies address and SELECT information to themultiplexers 166 and 168.

Port 1 of the microcomputer 154 provides a plurality of functions.Control of the ADC 156 is provided by a line 180 from port 1 to aswitching transistor 182 which varies the reference voltage supplied tothe ADC. Input to the ADC 156 from the multiplexer 158 is controlledthrough a line 184 from port 1 to a switching transistor 186 toselectively ground the multiplexer output to the ADC 156 under controlof the program of the microcomputer 154 as will be describedhereinafter. Grounding of the multiplexer 158 output while either of thepeak detectors 160 and 162 are selected causes a reset of the peakdetectors.

Address information allowing the multiplexer 158 to select from itsvarious input sources 160, 162, 164, 166, 168 or 170 is provided fromport 1 of the microcomputer through address lines 188.

Control of the trip coil 22 is provided from the microcomputer 154through port 1 and a TRIP line 190. Thus, when it is determined that atripping operation is called for, the microcomputer 154 sends, throughport 1, a signal on the trip line 190 causing the switching transistor192 to energize the trip coil 22, activate the mechanism 20, andseparate the contacts 18.

3. Operational Modes

Mode 1: Low Power

This mode is performed under conditions of very low current flow throughthe breaker (less than 25% of frame rating), when external power is notbeing supplied to the trip unit. Under these conditions sufficientoperating power cannot be continuously supplied to the trip unit, andsome of its normal functions cannot be reliably performed. Therefore,the power supply generates a pulse of operating power to the trip unitcircuitry sufficient to execute the normal operating cycle of the tripunit but to display only the present phase current through the breakeron the numeric display 80. This value is flashed by the display at arate which increases as load current increases. At load current valuesabove 25% of frame rating, Mode 2 operation is performed. Fractions ofrating values will hereinafter be indicated by per unit notation; e.g.25%=0.25 PU.

Mode 2: Normal

This mode of operation is performed when load current is greater than0.25 PU of frame rating but less than 1.0 PU of the rating plug value,or when external power is being supplied to the trip unit.

As can be seen in FIG. 5, the trip unit panel contains a number ofadjustment potentiometers, light-emitting diode indicators (LED's),pushbutton switches, and two-position switches. The panel also includesa pair of numeric display indicators 80 and 82. The electronic circuitryinternal to the trip unit causes the numeric display indicators 80 and82 to sequentially display the present value of electrical conditions onthe circuit being protected and the various limit settings defining thetime-current trip curve of the breaker as currently set. The LED's, whenlighted, indicate by the legends associated with each indicator, whatvalue is being displayed at any time by the numeric displays 80 and 82.If so desired, the numeric values displayed on the numeric indicators 80and 82 may also be sent to a remote location via the SERIAL OUT terminalof the Data I/O System 174 (FIG. 14).

Beginning at the top of the trip unit panel as shown in FIG. 5, the LEDindicator 84 is labeled PHASE CURRENT on the left and GROUND CURRENT onthe right. When this LED is lighted, it indicates that the present perunit value of current flowing in the three-phase circuit being protectedis displayed in the left-hand numeric display indicator 80, and thepresent per unit value of ground current on the circuit being protectedis indicated in the right-hand digital display indicator 82. In asimilar manner, the LED 86 is labeled PEAK KW SETTING and PEAK KW SINCELAST RESET. When this LED is lighted, the value appearing in theleft-hand numeric display 80 is that value of kilowatts delivered by thecircuit being protected which will cause a DEMAND signal to be generatedby the data input/output system. The peak value of kilowatts drawnthrough the breaker since the display was last reset (by the pushbutton105 immediately to the right) is presented on the numeric displayindicator 82. The LED's 88 and 90 correspondingly indicate PRESENT KWand MW×HOURS, and power factor multiplied by line voltage as follows:

    ______________________________________                                        PRESENT KW =                                                                  present phase current ×                                                                 (power factor × line voltage)                                           .BHorizBrace.                                                                 as entered by operator on                                                     front panel                                                   actual megawatt-hours = (MW × HOURS) × frame                      ______________________________________                                        rating                                                                    

    actual megawatt-hours=(MW×HOURS)×frame rating

In this manner, a user can more readily perform energy management forhis system. Not only is a continuous display of present demand, peakdemand, and total energy usage provided, but in addition, alarming orautomatic load shedding may be initiated by the output signal providedthrough the data I/O system in response to the PEAK KW monitoringfunction.

If desired, a potential transformer could be added to the circuitbreaker 10 to monitor line voltage and eliminate the need for manualoperator entry of a value of line voltage. Furthermore, a high-speed A/Dconverter could be added to sample line voltage and phase current at ahigh enough rate to permit direct calculation of power factor andeliminate the need for an operator to enter the power factor.

Below the rating plug 78 in FIG. 5 can be seen a number of LED's labeledINSTANTANEOUS, LONG DELAY, SHORT DELAY, and GROUND FAULT. To the left ofthis series of LED's is the legend CURRENT PICK-UP and to the right isthe legend TIME IN. When the LED 92 labeled INSTANTANEOUS is lighted,this indicates that the value of current which will result in aninstantaneous trip is presently being displayed in the left-hand digitaldisplay indicator 80. By definition, the instantaneous trip will occurimmediately, thus there is no corresponding time to be displayed, andthe display 82 is blank. When the LED 94 labeled LONG DELAY is lighted,this indicates that the left-hand numeric display indicator 80 ispresently showing the current value at which a long-delay trippingoperation will be initiated, while the right-hand numeric displayindicator 82 is showing the time parameter in seconds of a long delaytripping operation. These time and current values correspond to the longdelay tripping operation discussed above with regard to the time-currenttripping curve of the circuit breaker.

When the LED 96 labeled SHORT DELAY is lighted, the left-hand numericdisplay indicator 80 is showing the current value which will cause ashort delay tripping operation to be initiated, while the right-handnumeric display indicator 82 is showing the duration, in cycles, of ashort delay tripping operation. Similarly, when the LED 98 labeledGROUND FAULT is lighted, the left-hand numeric display 80 will show thevalue of ground current which will cause a ground fault trippingoperation and the right-hand digital display 82 will show the number ofcycles between the detection of the ground fault current and the commandto cause the circuit breaker to trip.

As can be seen in FIG. 5, some of the legends have a solid circularsymbol associated therewith, while other legends are associated with asolid square symbol. The circular symbols indicate that the parameterdesignated by the associated legend will be displayed as a per unitmultiple of frame rating. Similarly, those parameters associated with asquare symbol will be displayed as per unit multiples of plug rating.For example, assume the displays 80 and 82 were presenting values of0.61 and 0.003, respectively, and the LED indicator 84 is lighted. Thisrepresents a present phase current of 976 amperes (0.61×framerating=0.61×1600 amps=976) and a present ground current of 3.6 amperes(0.003×plug rating=0.003×1200 amps=3.6 amps).

A pair of miniature switches 102 and 104 labeled I² T RESPONSE are usedto vary the shape of the time-current tripping curve in the short delayand ground fault areas, respectively. When the switches 102 and 104 arein the lower position, this indicates the Ground Fault and Short Delayportions of the curve will not exhibit an I² T slope, but will insteadbe horizontal. When the switches 102 and 104 are in the upper position,the I² T characteristic will be employed, and the characteristic for theShort Delay tripping operation will have the shape as shown in FIG. 4.

A potential transformer connected to the associated circuit could beused to otain line voltage data, and rapid sampling and directmultiplication of the instantaneous values of phase current and linevoltage used to calculate real power. However, the disclosed methodprovides a convenient and cost-effective method which avoids isolationproblems associated with potential transformers.

Summarizing, in normal operation, the following operations will becalculated sequentially, with the entire calculation sequence repeated60 times per second: peak KW, MW-HR integration, instantaneous trip,long delay trip, short delay trip, and ground fault trip.

In addition the following values will be displayed sequentially inpairs, with each display lasting 4 seconds: PRESENT PHASECURRENT-PRESENT GROUND CURRENT, PEAK KW setting (demand)-PEAK KW SINCERESET, PRESENT KW-MWHR, POWER FACTOR×LINE VOLTAGE, INSTANTANEOUSPICKUP-TIME, LONG DELAY PICKUP-TIME, SHORT DELAY PICKUP-TIME, AND GROUNDFAULT PICKUP-TIME.

Mode 3: Overcurrent and Trip Mode

This mode is performed when either phase current is above the Long DelayPickup value or ground current is above the Ground Current Pickup value.Sequencing of display values and LED indication thereof continues as inMode 2 even though the breaker is overloaded. In addition, the LongDelay Pickup LED 94 will be lighted.

If the overcurrent or ground fault condition persists, the trip unitwill initiate a tripping operation according to the time-current tripcharacteristic loaded therein by the user. When tripping occurs, thefunction which initiated the trip (long delay, short delay,instantaneous, or ground fault) will be indicated on the front panel byenergization of the appropriate LED 92, 94, 96, or 98. The cause-of-tripinformation will be sent out by the data I/O system to the remoteindicator 145. In addition, the per unit phase or ground fault currentthat caused the trip will be displayed and frozen on the numeric display80.

In addition to the microcomputer trip capability, the trip circuitbreaker includes the thermal switches 141 as a back-up system. Shouldthis system initiate a trip operation, the Instantaneous LED 92 will belighted, a value of 15.93 PU current value will be displayed on thenumeric display 80, and an INSTANTANEOUS signal sent by the data I/Osystem.

Mode 4: Parameter Adjustment

As can be seen in FIG. 5, the trip unit panel also includes a pluralityof limit value potentiometers associated with the various legends on thetrip unit panel. These potentiometers are provided to allow an operatorto adjust the circuitry of the trip unit to vary the shape of thetime-current trip curve and produce the type of tripping characteristicsrequired by the design of the entire electrical distribution system.When an operator adjusts one of the potentiometers (for example, theINSTANTANEOUS CURRENT PICK-UP potentiometer 112) this adjustment isdetected by the trip unit circuitry and the sequential display of valuesis interrupted. The parameter value being adjusted is immediatelydisplayed in the corresponding numeric display indicator, and thecorresponding LED indicator is lighted. For example, if it is desired toadjust the instantaneous current pick-up value, an operator inserts ascrewdriver or other tool into the potentiometer 112 and begins to turnit. Immediately, the INSTANTANEOUS LED indicator 92 lights and thepresent value of the instantaneous current pick-up is displayed in thenumeric display indicator 80. This number is in per unit format, thatis, a multiplier times the frame rating, as specified by the solid roundsymbol. Thus, as the potentiometer 112 is rotated, the value displayedin the indicator 80 would begin to slowly increase in discrete stepsfrom, for example, 1.00 up to the maximum allowable value as storedinternally in the trip unit, which is 10.0. When the desired value isachieved, adjustment of the potentiometer is ceased and the trip unitresumes its sequential scan and display of present values and settings.In a similar manner, any of the potentiometers on the trip unit frontpanel may be adjusted to achieve the desired parameter setting.

In the past, adjustment of parameter values using potentiometers inconjunction with digital circuitry has presented problems. There was atendency, for example, for each minute change in the value of apotentiometer to produce a different value which would be immediatelydisplayed. This produced an annoyingly rapid variation of the displaywhich rendered adjustment difficult. Furthermore, temperature variationsand other minor perturbations in the circuitry would cause variation inthe display and value of the potentiometer even when no adjustment wasbeing made. In addition, failure of the potentiometer in the past wouldsometimes prevent the designated parameter from being read at all.

In order to avoid these problems, the present invention employs thepotentiometers to select one of eight predetermined parameter valuesstored within ROM of the trip unit microcomputer. Thus, thepotentiometer acts as a discrete multiposition switch rather than acontinuously variable adjustment device. In the event of a potentiometerfailure, the trip unit selects the most conservative value of theparameter associated with the malfunctioning potentiometer for use inits monitoring functions.

To add further convenience to an adjustment operation, the trip unitincludes a hysteresis feature which is described in detail in SectionIII.C.

Parameters may also be entered by an external circuit over the SERIAL INterminal (FIG. 14) of the data I/O system 174.

Mode 5: Test Mode

A TEST mode is also provided in the trip unit herein disclosed. Bypressing either of the momentary-contact pushbutton switches 128 or 130,an overcurrent condition or ground-fault condition, respectively, may besimulated. If the switch 106 is in the NO TRIP position, the faultcurrent value to be simulated is determined by the adjustment of thepotentiometer 120 while either of the switches 128 or 130 are depressed.With the switch 106 in the TRIP position, fixed values of fault currentare simulated. This simulated overcurrent or ground-fault condition willor will not result in actual opening of the contacts 18 of the circuitbreaker, as determined by the setting of the TRIP/NO TRIP switch 106. Ineither case, the test is initiated upon release of the pushbuttons 128or 130, causing the TEST MODE LED 100 to be lighted. When the delayperiod expires, the appropriate LED 92, 94, or 96 will light, thusindicating the successful completion of the test. If the switch 106 hasbeen set to the TRIP position, the contacts of the circuit breaker willactually open.

Through the use of the TEST mode with the switch 106 in the NO TRIPposition, an operator can check any desired point on the time-currenttripping characteristic. He does this by pressing the desired testbutton 128 or 130, and dialing in, on the TEST potentiometer 120, anydesired multiple of the maximum continuous current. He then releases thedesired phase or ground fault test button 128 or 130. The trip unit willsimulate a fault at that level of the multiple of maximum continuouscurrent which was entered via TEST potentiometer 120, and will simulatea tripping operation without actually opening the contacts.

At the completion of the test, LED 92, 94, 96 or 98 will be lighted toindicate whether the breaker tripped under instantaneous, long delay,short delay, or ground fault modes. The display 80 will show the perunit current value at which the breaker tripped (which will be the sameas the value entered via potentiometer 120) and display 82 will show thenumber of seconds or cycles (which is specified by LED's 92, 94, 96 or98) following initiation of the test in which the breaker tripped.

During execution of a test, a determination is made as to which islarger: actual phase (or ground) current or simulated phase (or ground)current, and the larger of the two compared to the various settingvalues. Thus, a test can take place with no loss of protection.Furthermore, if simulated current is larger than actual current, butboth are larger than Long Delay Pick-Up, a trip operation will beperformed at the end of the test, regardless of the position of theTRIP/NO TRIP switch 106.

The operator can then plot the time-current value displayed to see ifthis point lies on the desired time-current tripping characteristiccurve. Any number of points can be so tested, allowing completeverification of the tripping characteristic as entered in the trip unit.

C. Remote Indicator And Power Supply

A remote indicator and power supply 145 may also be connected to thetrip unit 26. This device, shown schematically in FIG. 9, provides thecapability of indicating at a location remote from the circuit breaker10 when the breaker has tripped and what caused the trip. In addition,the device 145 can indicate when peak power demand has exceeded a presetlimit. These indications are provided by four LED's corresponding toPEAK KW DEMAND EXCEEDED, OVERCURRENT TRIP (long delay), SHORT CIRCUITTRIP (instantaneous, short delay, or thermal), and GROUND FAULT TRIP.

Two relays are also provided in the remote indicator 145. One relay isactuated on receipt of a peak KW demand indication, to provide thecapability of automatic load shedding. The other relay is actuated onreceipt of any type of trip indication to trigger an alarm bell, light,or other desired function.

The device 145 also includes a power supply energized from the AC linewhich provides 32 volts DC. The output of this power supply is connectedto the EXTERNAL DC terminal 148 of FIG. 2.

A detailed description of the circuitry of the remote indicator andpower supply is contained in Section III.E.

III. ELECTRICAL DESCRIPTION

A. Arithmetic, Logic, and Control Processor

The arithmetic, logic, and control processor 154 is a type 8048microcomputer manufactured by the INTEL Corporation. As seen in FIG. 5A,the single 40-pin package includes the following functions: an eight-bitarithmetic logic unit 153, a control unit, a 1 K×eight-bit ROM programmemory 155, 64×eight-bit RAM data memory 157, an eight-bitbi-directional data bus 172, and two quasi bi-directional eight-bitports Port 1 and Port 2. Additional control lines are also provided. Amore detailed description may be obtained from the previously referencedMCS-48 Microcomputer Users Manual. Referring to the figures, andespecially FIG. 2, the interconnections to the microcomputer 154 willnow be described.

The eight-line data bus 172 is connected to the eight output terminalsof the ADC 156. The eight-bit digital values supplied by the ADC arethus read by the microcomputer 154 by the following sequence: a pulse issent out on the WR line of the microcomputer 154 to the ADC 156,commanding the ADC to convert the analog quantity appearing at its inputterminals into an eight-bit digital quantity. Upon completion of theconversion process, the ADC 156 generates a pulse over the lineconnected to the T1 test terminal of the microcomputer. Themicrocomputer then generates a pulse on the RD line, which transfers thebit pattern produced by the ADC to the accumulator of the microcomputer154.

The data bus 172 is also connected to the data input/output system 174,to allow the trip unit 26 to communicate with other circuit breakers andwith the remote indicator/power supply 145. The data input/output systemwill be more completely described in Section IIIG.

Port 1 and port 2 of the microcomputer provide the capability tocommunicate and control the other components of the trip unit 26. Thespecific connections will now be described. Line numbers correspond tothe notation used in the MCS-48 Microcomputer Users Manual.

Port 1:

Line 0, line 1, line 2--These lines provide the channel addressinformation from the microcomputer 154 to the multiplexer 158, asindicated at 188 on FIG. 2.

Line 3--This line, indicated at 180 in FIG. 2, actuates the FET 182 tochange the reference voltage delivered to the ADC 156, therebyincreasing the resolution for the Long Delay phase current measurement.

Line 4--This line activates the transistor 192 to energize the trip coil22 and cause the mechanism 20 to open the contacts 18 to the breaker.Line 4 is indicated at 190 in FIG. 2.

Line 5--This line actuates the FET 186 to ground the output of themultiplexer 158, which also grounds the individual input to themultiplexer 158 which happens to be selected at that time. Thus,activating line 5, (indicated at 184 in FIG. 2) can reset the peakdetectors 160 and 162, when these are selected by the multiplexer 158.

Line 6--This line activates the Chip Select terminal on the external ROMwhen performing a read operation.

Line 7--This line, indicated at 178 in FIG. 2, periodically energizesthe power supply 176 of the data input/output system 174.

Port 2:

Line 0, Line 1, Line 2, Line 3--These lines carry the data sent from themicrocomputer 154 to the panel display system 155. As can be seen inFIG. 6, the digit values are supplied over these lines to the latchdecoder 194 for display on the numeric indicators 80 and 82. Line 0,line 1, and line 2 (indicated as 207 in FIG. 6 and FIG. 7) also supplychannel address information to multiplexers 206, 166 and 168. Line 3(indicated as 216 in FIG. 7) is connected to the INHIBIT terminals ofthe multiplexers 166 and 168 and serves to toggle or selectivelyactivate the multiplexers 166 and 168.

Line 4--This line, identified as 200 in FIG. 6, actuates the transistor198 to light the decimal point on the numeric indicators 80 and 82.

Line 5--This line is connected to the Latch Enable terminal of the latchdecoder 194 and serves to latch the data values appearing on lines 0through 3 in the latch decoder 194.

Line 6--This line energizes the transistor 208 which, in conjunctionwith the output lines of the latch decoder 194 serves to energize theLED indicators 84 through 98.

Line 7--This line is connected to the INHIBIT terminal of multiplexer206 and is indicated at 212 in FIG. 6.

The Interrupt terminal INT of the microcomputer is connected to the highvoltage side of the thermal switches 141. Activation of these switchesthus causes the Interrupt terminal 143 to go LO and initiate theInterrupt instructions in ROM 155 which processes the thermal tripoperation, and indicates an instantaneous display trip.

B. Panel Display System

A detailed schematic diagram of the panel display system of FIG. 2 isshown in FIG. 6. As can be seen, a seven-segment latch decoder circuit194 such as a type CD4511B is provided. A four-bit input signal isprovided by lines 0-3 of port 2 of the microcomputer 154. The decodercircuit 194 provides a seven-line output signal through a load resistorarray 196 to the pair of four digit seven-segment LED digital displayindicators 80 and 82. An eighth line for activating the decimal point ofthe digital display indicators 80 and 82 is also provided through atransistor 198 which is actuated by a line 200 also connected to port 2of the microcomputer 154. A driver circuit 202 and transistor 204 areprovided under control of a multiplexer circuit 206, which may be forexample, a type CD4051B. A three-bit SELECT signal, also driven by threelines 207 from port 2 of the microprocessor is supplied as input to themultiplexer circuit 206. The LED indicators 84, 86, 88, 90, 92, 94, 96,98 and 100 are actuated through the transistor 208 by a line from port 2of the microcomputer 154 in conjunction with the digital displayindicators 80 and 82. The TEST LED 100 is also driven by the transistor208 and an additional transistor 210 in conjunction with an INHIBIT line212 also supplied to the multiplexer 206 from port 2 of themicrocomputer.

C. Parameter Input

Limit values for the trip unit 26 are provided by the potentiometers108-120, as shown in FIGS. 2, 5, and 7. Each of the potentiometers hasone end of its resistance element connected to the V_(REF) supply, andthe other end of the resistance element grounded. The wiper of eachpotentiometer is connected to an input terminal of one of themultiplexers 166 and 168 which may be, for example, a type CD4051B.Thus, each of the potentiometers provides an analog voltage signal toits appropriate multiplexer input terminal. These input terminals areselected by a three-bit address line 207 plus an INHIBIT line 216connected to port 2 of the microprocessor.

The two-position switches 102, 104 and 106 correspond respectively to I²T IN/OUT switches for phase current and ground current, and a TRIP/NOTRIP function for the test mode. As can be seen, these switches serve toconstruct a variable voltage divider between V_(REF) and ground whichprovides any of six analog voltage values to a terminal of themultiplexer 168. In a similar manner, the pushbutton switches 107, 105,128 and 130 corresponding respectively to DISPLAY RESET, DEMAND RESET,PHASE TEST, and GROUND TEST, serve to place any of eight analog voltagesignals on another terminal of the multiplexer 168.

D. Style Number Designator

FIG. 8 shows in detail the style number designator circuit 170 shown inFIG. 8. Each four-digit decimal style number corresponds to a particularoption combination. As can be seen in FIG. 8, the style designatorcircuit provides input to four terminals of multiplexer 158. Each ofthese terminals represents one digit of the decimal style number and maybe connected to any of four positions on a voltage divider formed by theresistors 218, 220, and 222 connected between ground and V_(REF). Theseconnections are selected and made by jumper connections wired at thefactory to provide each of the terminals of multiplexer 158 with any offour possible analog voltage signal values. The multiplexer 158, oncommand, then supplies these values to the ADC 156 which converts themto the 8-bit digital code which is read by the microcomputer andinterpreted as the style number, allowing the microcomputer to determinewhich of the many option combinations for the trip unit 26 are actuallypresent in that particular trip unit.

E. Remote Indicator And Power Supply

The data input/output system 174 supplies pulse coded output signals,over a single optically coupled pair of wires, to the Remote Indicator145 shown in FIG. 9 providing a remote indication that the load beingsupplied through the circuit breaker has exceeded a predetermined powerlimit. In addition, cause-of-trip indications of overcurrent, shortcircuit, or ground fault are provided. The circuit to be describeddecodes the corresponding four input signals to provide both LEDindications and relay closures.

In addition, the circuit provides a remote source of power, from boththe AC line and from batteries, to the power supply 144. This capabilityis needed in those applications which require continuous retention ofdata such as cause-of-trip indicators and energy functions includingmegawatt-hours and peak demand power.

As can be seen in FIG. 9, input power is supplied through a transformer602, rectifier circuit 604, and filter capacitor 606 at a level ofapproximately 32 volts. A current limiting resistor 608 is provided toprotect against accidental shorting of the output terminal 610. Terminal610 is connected to the EXTERNAL DC INPUT 148 (FIG. 2) and terminal 612is connected to the digital ground terminal of the trip unit 26. If ajumper is connected between terminal 610 and terminal 614, the threeinternal 8-volt nickel-cadmium batteries 616 can be activated to supportthe output voltage at 24 volts, should the AC input voltage beinterrupted. A 10 K "trickel charge" resistor 618 is provided forbattery charging.

An 8.2 volt power supply is provided by resistor 620, Zener diode 622,and capacitor 624 for the decoding and alarm circuit.

The data I/O output terminal 508 of FIG. 14 labeled Remote Indicator Outis connected to terminal 626 of FIG. 9, and the I/O COMMON terminal 500of FIG. 14 is connected to terminal 628 of FIG. 9. The 100 microsecond,4 volt output pulses applied to terminals 626 and 628 produce an 8milliampere current flow through the optical coupler 630. This currentturns on the coupler transistor which produces an 8 volt pulse acrossresistor 632.

The microcomputer 154 can produce one 100 microsecond pulse every twomilliseconds, or a maximum of eight pulses per cycle of AC power. Acoding technique is used, with one pulse out of eight denoting a DEMANDalarm. If a trip has occurred, two consecutive pulses out of eightdenote a ground fault trip, three consecutive pulses out of eight denoteovercurrent (long delay) trip, and five consecutive pulses out of eightdenote a short circuit (either instantaneous or short delay) tripcondition. The pulse coding scheme is shown as waveforms A in FIG. 10.

The input pulses provide trigger inputs for a retriggerable 3millisecond monostable flip-flop output Q1 of integrated circuit 634which may be, for example, an RCA CD4098 device. The retriggerablefeature means that any pulse which occurs during the 3 millisecondtiming interval will cause a new 3 millisecond interval to start.Waveforms B of FIG. 10 show the resulting Q1 output for one, two, three,and four consecutive input pulses, corresponding to a DEMAND ALARM, aground fault trip, a long delay trip, and a short circuit trip,respectively. The amplitude of the Q1 pulses is equal to the supplyvoltage supplied to the integrated circuit 634. When the Q1 output isaveraged by resistor 636 and capacitors 638, a DC voltage C is producedwhose value is the following fraction of the supply voltage; either 3/16volts, 5/16 volts, 7/16 volts, or 11/16 volts, respectively. This valueis fed to the inverting input terminals of quad comparator 640 whichcompare the filtered value C to fixed fractions of the supply voltage of1/8 volts, 1/4 volts, 3/8 volts, and 9/16 volts, which are developed bythe divider network including resistors 642, 644, 646, 648, and 650. Thecomparator then provides outputs which indicate which of four possiblepulse patterns were applied at input terminals 626 and 628. If, forexample, a DEMAND condition exists, producing a pulse pattern of one outof eight pulses, the DC voltage at the inverting terminal of comparatorA of 640 will be 3/16 of the supply volts, which is greater than 1/8 ofthe supply volts but smaller than 1/4 of the supply volts. As a result,the output terminal of comparator A will be LO while other inputs willbe HIGH. Transistor 652 and relay 654 will be turned on by current flowthrough resistor 656 which also lights the demand LED 658.

An overcurrent trip condition will cause three consecutive pulses toappear at the input terminals 626 and 628, and an averaged value of 7/16of the supply voltage will appear at the inverting terminals of thecomparators of 640. This value is greater than 3/8 of the supply voltsbut less than 5/8 of the supply volts. In this case, the outputterminals of comparators A, B, and C will be LO. Transistor 660 andrelay 662 will be on, because of current flow through the overcurrentLED 664 and resistor 666. Transistor 652 and the DEMAND LED will be offbecause of the shorting effect of transistor 668. The GROUND LED 670 isalso off because of the shorting effect of the OVERCURRENT LED 664. Inthis way, the highest level comparison always dominates. A function ofintegrated circuit 672 (which may be, for example, an RCA type CD040)and Q1 is to provide a 1/2 second ON delay for the comparators, which isrequired to allow the voltage on capacitor 638 to stabilize. The Q1pulses occur every 1/60 seconds. These are counted by counter 672 untilthirty-two pulses occur and output Q6 goes HIGH. At this time, output Q1is turned on, and additional pulse inputs are inhibited by diode 674.

Approximately 30 milliseconds after the last pulse is received byoptical isolator 630, the Q2 terminal of the retriggerable monostableflip-flop 634 will go HIGH. This resets the output Q6 of 672 and turnsQ1 off. The function of counter 672 and Q1 is to provide positive on/offoperation of the LED indicators and the ALARM/LOCK-OUT and DEMAND RELAYS662 and 654.

F. Data Input/Output System and Associated Power Supply

As hereinbefore explained, it is contemplated that a circuit breakeremploying the principles of the present invention will be employed in anelectrical distribution system in coordination with a number of othercircuit breakers. It is sometimes desired that various commands andinformation be sent from this circuit breaker and that variousparameters sent by other associated breakers be sensed by this breaker.This information is used to construct the desired interlocking scheme asspecified by the system architect or designer.

The Data I/O System, shown in detail in FIG. 14, includes four outputlines: Short Delay Interlock Out 502, Ground Interlock Out 504, SerialOut 506, and Remote Indicator Out 508.

Three input terminals are also provided: Short Delay Interlock In 510,Ground Interlock In 512, and Serial In 514. The Serial Out and Serial Interminals are used to communicate digital data between the microcomputer154 and a remote digital circuit. The Remote Indicator Out terminalprovides a one-of-four coded pulse output for cause-of-trip indication(overcurrent, short circuit, or ground), and peak power demand alarmindication to the Remote Indicator, as described in Section III F. Theinput and output interlock terminals allow direct interlock connectionsbetween breakers without any additional components.

If typical optical coupling circuitry were used, 400 milliwatts of powerwould be required (12 milliamperes at 5 VDC for each of seven lines).The power which the current transformers 24 are capable of supplying isonly about 500 milliwatts (100 milliamperes at 5 VDC), most of which isrequired by the microcomputer 154. Conventional optical couplingcircuitry thus cannot be used.

The power supply for the data input/output system 174 includes a pulsetransformer 501 connected through a transistor 228 to line 7 of port 1,indicated as 178 in FIGS. 2 and 14. The microcomputer provides a 100microsecond pulse every 2000 microseconds, as commanded in the commondisplay subroutine, thereby reducing the power supply requirement of thedata input/output system 174 by a factor of nearly 20 to 1, or about 20milliwatts (4 milliamperes average at 5 VDC). This is small enough to beeasily supplied from the power supply 144.

The waveforms appearing in the power supply 176 are shown in FIG. 15.Waveform A is that generated on line 7 of port 1 by the microcomputer154. For approximately 100 microseconds out of about every 2000microseconds (actually 1/8×1/60 seconds) line 7 of port 1 is held low atmicrocomputer circuit ground. This turns on transistor 228, therebyapplying +5 volts to the input of transformer 501, as seen in waveform Bof FIG. 15. A corresponding waveform is produced on the output terminalof transformer 501 relative to the system common terminal of the datainput/output system 174.

If an output is desired from, for example, the Remote Indicator Outterminal 508, the corresponding microcomputer output line, line 3 of thedata bus 172 is held at circuit ground, as shown in waveform C in FIG.15. LED 516 is turned on by current flow through transistor 228. Thephototransistor 517 then turns transistor 518 on, producing outputvoltage waveform D. If line 3 of data bus 172 (waveform C) is HIGH, thenthe corresponding output from transistor 518 is zero, as shown bywaveform D.

The input circuitry is designed to work with both a directly coupled DCsignal from an older circuit breaker, or a pulse input such as thatpreviously described in this section. An input signal at, for example,the Serial Input terminal 514 as shown in waveform E, will also appearat the gate of FET 236, as shown in waveform F. When the pulse voltageappears at the output of pulse transformer 501, current will flow in LED238, and then through FET 236 which has been turned on by the inputsignal at the Serial Input terminal 514. The FET 236 has a turn-on gatevoltage of 2.5 volts and internal gate-to-source 15 volt Zener diodeprotection. This range is required to meet the 4 volt pulse inputprovided by a microcomputer type circuit and a 12 volt DC signalprovided by the older type of solid state trip unit.

FET 236 provides two functions. First, it provides a memory element whenthe input signal is a pulse. It does this is connection with thecapacitor 232 which is charged through resistor 230 by the 100microsecond input pulse. The values of capacitor 232 and resistor 230are chosen so as to give a 15 microsecond time constant. Capacitor 232discharges through resistor 234, sized to give a 10 millisecond timeconstant. The capacitor 232 cannot discharge through 230, since theinput signal is provided by the emitter of an NPN transistor. Thus, thegate of transistor 236 is held high as long as input pulses occur everytwo milliseconds. Approximately 10 milliseconds after the input pulsesdisappear, transistor 236 will be turned off.

The second purpose of transistor 236 is current gain. The opticalcoupler 226 requires nearly 10 milliamperes to turn the associatedphototransistor on. This current is provided by transistor 236. The highDC input impedance at the input terminal is required, since the oldertrip unit control circuits can provide only a small DC input current.

The presence or lack of an input signal on terminal 514 is read by themicrocomputer at line 0 of the data bus, waveform G, which is highduring the 100 microsecond pulse period if, and only if, an input signalis present at the terminal 514. A pull-down resistor 237 is provided tomaintain the data bus lines connected to the data input terminals atcircuit ground when no input signal is present at the terminal 514. Inthis manner, a signal from a circuit breaker, emergency power generator,or other associated component of the electrical power distributionsystem can be sensed by the microcomputer 154 and the circuit breaker 10can be commanded to perform appropriate action. Furthermore, parametervalues can also be supplied, through the SERIAL IN terminal 514, from aremote location. Appropriate instructions in ROM then decode theincoming information and store it in RAM for use by the limit checkingfunctions.

G. System Power Supply

1. Block Diagram Description

The power supply 144 of FIG. 2 is shown in block diagram form in FIG.11. It can be powered by one of four sources: external AC or DC voltage,the Remote Indicator 145 of FIG. 2, current input from a ground currentdetection transformer 28, or current input from the three phase currentmeasuring transformers 24.

The rectified output of the external AC source is compared to the DCvoltage from the Remote Indicator and the largest instantaneous value issupplied by the auctioneer circuit 702 to the power supply's energystorage capacitor 704 for use by the DC-to-DC converter 706 and the tripcoil 22. A voltage sensing circuit 708 monitors the output of thevoltage auctioneering circuit 702. Whenever this voltage is greater than22 VDC the DC-to-DC converter 706 is turned ON. A crowbar current switch710 is thrown to position (2) when the voltage exceeds 24 VDC. Theconverter 706 provides the 5 VDC supply (at 100 mA) for themicrocomputer circuit, a reference voltage V_(REF) (1.64 VDC) and apower ON reset control signal RS.

The unit can also be powered by either the rectified output of theground current transformer or the current auctioneered, rectifiedoutput, of the three phase current transformers 24. The two currents aresummed at 712 and fed to the "crowbar" 710 which passes the currenteither into the energy storage capacitor 704 or a current bypass 714.Current flows into the capacitor 704 until the capacitor voltage reachesabout 39 VDC, at which point the "crowbar" 710 transfers the current tothe by-pass circuit 714. Current by-passing continues until the voltageon the capacitor 704 drops to about 34 VDC and the switch 710 againcauses the current to flow into the capacitor.

2. Circuit Description

The power supply 144 is shown in greater detail in FIG. 12. The externalAC input is rectified by BR201 and compared to the external DC input.The result is fed through D101 to energy storage capacitors C105 andC112. The sensed voltage is also fed to the crowbar circuit formed bythe power field effect transistor Q101 and gates A and B (connected asinverters) of quad NAND circuit Ic101. The quad NAND circuit is poweredby current flow through R103, D107, D108 and D109, which produces atemperature stabilized voltage of about 10 VDC for pin 14 of ID101D. Thequad NAND has input hysteresis which causes the output to go LOW whenthe inputs exceed about 70% of the supply voltage (7 VDC). The outputthen stays low until the inputs drop to 30% of the supply voltage (3VDC). Thus the crowbar is turned ON when 7 VDC appears across R105 whichcorresponds to 24 VDC at the external DC input (7 VDC plus drop acrossR104, R102, and D103). It will be noted that the crowbar can also beturned ON if the voltage across the energy storage capacitor 704 exceeds39 VDC.

If external power is available, then the on-off status of the converter705 is controlled by the external power supply voltage, rather than thestorage capacitor voltage.

The 24 VDC switching point for the external DC input corresponds to theminimum DC voltage required for the trip coil 22 to operate. The 39 VDClimit on the voltage across the energy storage capacitor is a compromisebetween the 50 VDC maximum limit of the capacitor and the 30 VDC minimuminput to the converter required to produce 5 VDC output at 100 mA DCwith a minimum current transformer output 32 mA RMS.

Current shunts R100 and R101 are used to sense phase and ground currentrespectively. It will be noted that current flow through the resistorsis through either Q101 (crowbar ON) or C105 and C112 (crowbar OFF) andIC102.

The required 15 millisecond turn-off delay of the +5 VDC supply isachieved by means of diode D110, resistor R107, and capacitor C102. Whenthe voltage at pins 8 and 9 of IC101 drops below 3 VDC the output pin 10goes high. A 15 millisecond delay exists before pin 12 and 13 reaches 7VDC. At this time pin 15 goes low causing the +5 VDC reference to go tozero.

The voltage sensor 708 also provides an ON/OFF control to the DC-to-DCconverter 706. The converter 706 is turned ON when the capacitor voltagereaches 37 VDC and OFF when it drops to 33 VDC. A 15 millisecond delayin the OFF signal is used to insure that the microcomputer 154 is ONlong enough to display the present value of phase and ground current,even when the output current from transformers 24 is too small tomaintain the operation of converter 706, and to ensure the maintenanceof a TRIP signal long enough to effect generation of the trip coil 22.Note that the trip coil is controlled by non-latching FET 192, ratherthan a latching device such as the SCR's used in the prior art. Thisprovides immunity from nuisance trips due to electrical transients, andprevents undue drain on the power supply when operating power issupplied by a battery.

The switching points of the ON/OFF control 708 and crow bar 710 areshown in FIG. 13.

The converter 706 is a chopper type consisting of PNP darlingtonswitching transistor IC102, inductor L101, "free wheeling" diode D112,and a voltage feedback reference formed by transistors Q103 and Q104.The voltage at the base of Q103 is adjusted to be +5 VDC by means ofR109. This voltage is approximately 1/2 the temperature stabilized +10VDC produced by D107, D108 and D109.

The circuit operates as follows. If the output voltage is below +5 VDC,Q103 will be ON and Q104 OFF. The collector current of Q103 is the basecurrent for the PNP darlington transistor IC102 which is then turned ON.With approximately +35 VDC applied to L101 the current will riselinearly. The current will flow into C106 and the connected load. Whenthe output voltage exceeds +5 VDC, Q103 will be turned OFF and Q104 willbe turned ON. The collector current of Q104 turns on Q102 which clampsthe base of IC102 causing it to be turned OFF rapidly. At this time, thecurrent in L101 will switch from IC102 to diode D112. The output voltagewill begin to decrease until Q103 turns ON, Q104 turns OFF, and theprocess repeats itself. Hysteresis in the ON/OFF switching results fromnatural over and under shoot associated with the L101 and C106 resonantnetwork. Positive switching feedback is provided by C103 and R110. Theswitching points of the power supply 144 are shown in FIG. 13.

In addition to the +5 VDC level, the power supply 144 also provides areference voltage V_(REF) which is used by the microcomputer 154. Anadditional signal, a power-on reset signal for the microcomputer isprovided by IC103 in combination R114, R115, R116 and C106. When theconverter turns ON and +5 VDC is produced the RS line remains at circuitground for about 5 milliseconds. This signal is applied to themicroprocessor which is then reset. Diode D111 provides an immediatepower-down reset as soon as the 5 VDC reference goes to zero, therebyassuring both a safe power-up and power-down transition.

H. Read-Only Memory

The internal microcomputer ROM 155 supplied with instructions defining aseries of eight major functions which are executed every cycle of ACcurrent, that is, every 16.667 milliseconds. Each function isresponsible for retrieving one or more parameter values from outside themicrocomputer. These parameters include values obtained from theelectrical circuit being protected, such as phase current and groundcurrent, as well as values specified by the front panel potentiometersand switches. The function then loads the parameter value into aspecified location in RAM. In addition, most of the functions are alsoresponsible for performing one or more limit checks; for example,comparing present phase current to the instantaneous trip pick-up value.Since the entire loop of eight functions is executed every 16.67milliseconds, each of the limit checks is performed at that rate.

In addition to the scanning and limit check duties, each function isresponsible for two operations relating to the front panel numericdisplays 80 and 82. Every four seconds, one function reads a displayparameter value from its assigned location in RAM. It then formats thisparameter value into four digit values. For example, if the presentphase current is equal to 2.14 per unit, the appropriate function wouldproduce four digit values: a blank, a two, a one, and a four. Thesedigit values would then be placed into assigned locations in RAM, eachlocation corresponding to one digit of the numeric display indicator 80.Generally, each function will so format two parameter values, thusloading a total of eight digit values into corresponding RAM locations.These digit values remain in RAM for four seconds until the nextfunction performs its digit value loading duty.

At this point, the digit values are residing in RAM; they must now besent to the appropriate digit of the numeric displays 80 and 82, thesecond operation performed by the eight main functions. Each function isresponsible, at each time it is executed, for retrieving one of thedigit values from RAM and sending this digit value out on port 2 of themicrocomputer 154 to the numeric displays 80 or 82. The digit value thenappears lighted in its appropriate location in the numeric displays.Since a new function is executed approximately every 2 milliseconds(16.667/8 ms), the digit value will appear for this length of time onthe numeric display before it is extinguished and the next digit valuesent to a different digit location on the numeric display. At any giventime, therefore, only one digit out of eight is lighted on the numericdisplays 80 and 82. However, the digits flash so rapidly that theyappear to an observer to be simultaneously lighted.

The external ROM 151 is optional and may be used to store instructionsto implement additional features such as other functions related to thedata I/O system. Also, the look-up table for potentiometer settings maybe stored in external ROM to facilitate changes in the table values.

The organization of the main instruction loop in ROM of themicrocomputer can be seen in FIG. 17. The eight main functions are namedFUNCTx, where x equals 1 through 8. The major subroutines called fromthese functions are the common display routine CMDIS, the analog todigital conversion routine ADCV1, the subroutine to toggle between thetwo display panel multiplexers 166 and 168 and perform the analog todigital conversion TADCV, and the subroutine to obtain discrete valuesfrom the potentiometer settings READ. The main functions, and thecorresponding subroutines will now be described in greater detail.

CMDIS - FIG. 26

This subroutine is called by each major function and thus is executedevery 2 milliseconds. It displays one digit value, as addressed byregister R1, and performs an analog to digital conversion on one of theeight input lines of the multiplexer 158, as specified by register R6.DMDIS outputs one pulse of 100 microsecond duration on line 7 of port 1,to energize the data input/output power supply 176. A portion of CMDIS,called TADCV, switches between multiplexer 166 and 168 to read apotentiometer from the other side of the panel. In addition, CMDIScompletes a time delay to ensure that each major function executes inexactly 16.667/8 milliseconds.

Reference may now be made to FIG. 26 for a more detailed description ofCMDIS. An internal counter is first checked to determine if the 16.667ms/8 execution time window has expired. If not, the subroutine loopsuntil the window does expire. The counter is then reset.

Next, line 7 of port 1 is activated to perform two functions. Theanalog-to-digital converter Chip Select terminal is deactivated by thisline. This line is also connected to transistor 228 of the datainput/output power supply. Thus, activation of line 7 of port 1constitutes the leading edge of an approximately 100 microsecond pulsefor the data I/O power supply.

Pre-existing alarm conditions are now checked to determine if a pulseshould be sent out on the serial output terminal of the opticallycoupled data input/output circuitry 174. As previously described, theserial output feature provides a pulse coded signal over a 16.667millisecond time window to inform the remote indicator of possible alarmor trip conditions.

Register 6 is now incremented to obtain the channel address for the nextinput line of the multiplexer 158 to be accessed. Register 1 is nowdecremented to obtain the address of the next digit value for display.

Using register R1 as an address pointer, one of the eight digit valuesis now retrieved from RAM and prepared for dispatching to the numericdisplay indicators. Since the digit value only requires four bits, theupper four bits are used to properly set up the Latch Enable line 5 ofport 2 and the inhibit line 7 of port 2 212. The LED indicator 84, 86,88, 90, 92, 94, 96, 98 or 100 corresponding to the parameter now beingdisplayed is controlled by bit 6 of port 2. The corresponding bit in thedigit value being displayed is set or reset by the SRACE subroutine inFUNCT1. This control information and the digit value are then sent outon port 2 to the latch decoder 194 of the display system 155.

The channel address for the multiplexer 166 or 168 as contained inregister 6 is now sent out on port 2. The analog to digital conversionroutine ADCV1 is executed, and the digital value of the input to themultiplexer 158 is stored in register 3 and in the accumulator.

FUNCT1--FIG. 18

This function first initializes register R1 with an address one greaterthan the address of DIGIT1, the digit value which will be displayed inthe rightmost position of the numeric displays 80 and 82 (which will bedecremented by CMDIS before used). It also initializes register R6 withthe first channel address to be accessed by the multiplexer 158.

Subroutine SRACE is entered next. This subroutine increments a foursecond counter. If this counter overflows from a hex value of FF tozero, this indicates that the four-second display period has elapsed,and it is time to command a new pair of values to appear on the numericindicators 80 and 82. This is done by shifting the register R7. Next,SRACE sets bit 6 in one of the eight digit value RAM locations so thatthe appropriate LED indicator corresponding to the parameters beingdisplayed will be lighted.

The common display routine CMDIS is now called. Upon completion, DIGIT1,the rightmost digit of the numeric display 82, will be lighted and thepresent phase current will have been read and processed by the ADC 156.The present phase current value is now stored in RAM.

Index register R7 is now checked to determine if it is time to displaythe present phase current value on the front panel numeric displayindicator 80. If so, the value of present phase current is formattedinto four digit values, and each of these digit values stored in thememory locations DIGIT8, DIGIT7, DIGIT6, AND DIGIT5 in RAM correspondingto the leftmost display digits, that is, the digits of the numericindicator 80. The present ground current is also formatted into fourdigit values. These digit values are stored in the RAM locations DIGIT4,DIGIT3, DIGIT2, and DIGIT1 corresponding to the values of the rightmostdigits, that is, the four digits of the numeric display 82.

Next, serial data I/O operations are performed, if called for, and thevalue of phase current used for the long delay function is read. Inorder to obtain a value having twice the resolution of the standardvalue of present phase current, the reference voltage supplied to theADC 156 is adjusted via line 6 of port 1. The ADC is now commanded toagain convert the value of the peak detector 160 as supplied through themultiplexer 158. Following the completion of the analog-to-digitalconversion, the capacitor of the phase current peak detector 160 isreset by grounding the output of the multiplexer 158 through FET 186, ascommanded by line 5 of port 1. The value of long delay phase current isnow stored in RAM.

FUNCT1 now sends a channel address to the multiplexer 158 via port 1 toselect the ground current peak detector 162. The analog to digitalconversion routine ADCV 1 is called to read the ground current andconvert it to a digital value. The ground current peak detectorcapacitor is now reset.

At higher levels of phase current, the ground current transformer 28 cangenerate fictitious values of ground current when no such value, infact, exists. This effect is more noticeable as phase current increases.Therefore, the fictitious ground current is accounted for by reducingthe value of ground current to be stored in RAM by a factor of 1/8 ofthe phase current whenever the phase current is between 1.5 per unit and9 per unit. If the present value of phase current is greater than 9 perunit, the ground current is neglected, by zeroing the present groundcurrent. The appropriate value of ground current is now stored in RAM.

FUNCT2--FIG. 19

This function determines the average phase current, performs energycalculations, and determines the style number of the trip unit 126.First, the multiplexer 158 is supplied an address via port 1, as indexedby register R6 to cause the averaging circuit 164 to supply an analogvalue to the ADC 156. The common display routine is now called, causingDIGIT2, the second digit from the right on the numeric display indicator82, to be lighted, and a digital value for the average phase current tobe supplied. The value of average phase current is next multiplied bythe product of power factor times line voltage, as specified by thefront panel potentiometer 110. The result is the Present Kilowatt value,PRKW. This value is temporarily stored and is also added to themegawatthour tally. A check is next made to determine if PRKW is greaterthan the peak kilowatt value registered since the last actuation of theKilowatt Reset pushbutton 105 (PKACKW). If PRKW is greater, the peakaccumulated kilowatt value is set equal to PRKW, and both values storedin RAM.

A check is next made on register R7 to determine if it is time todisplay the present kilowatt and megawatthour values on the numericdisplays 80 and 82. If so, these quantities are formatted into fourdigit values apiece and loaded into the digit value storage locations inRAM.

An address is now generated to the multiplexer 158 to select the stylenumber designator 170 to be supplied to the ADC 156. An A to Dconversion is now made on the style number and this value stored in RAM,to designate which of several optional features are included in thepresent trip unit and to select execution of the appropriateinstructions farther down in ROM.

FUNCT3--FIG. 20

The first task of this function is to reset the number of pulses to besent out over the serial output terminal. This information will later beused by the common display program to produce the proper pulse code onserial output. The common display routine is now executed, to lightDIGIT3, the third digit from the right on the numeric displays andreturn a digital value from the Peak Kilowatt setting potentiometer 108.

Next, a flag is set to prevent an extraneous pulse from being sent onthe serial output terminal. The READ routine is then executed to obtainone of eight discrete values for the Peak Kilowatt setting as specifiedby the corresponding potentiometer 108. This routine will be laterdescribed in greater detail.

A check is now made to determine if it is time to display the PeakKilowatt setting on the numeric indicator 80. If so, the value of PeakKilowatt setting as determined by the READ routine is formatted intofour digit values and stored in the digit value locations in RAMcorresponding to the digits of the numeric display 80.

A running tally of kilowatts is maintained in RAM. This tally isincremented by the present kilowatt value on every execution of FUNCT3,thus integrating the kilowatt values over time, producing a valuecorresponding to kilowatt hours. A check is now made of this location inRAM to determine if a value corresponding to 10 kilowatthours has beenreached. If so, a megawatthour tally in RAM is incremented and thekilowatthour tally reset retaining the remainder. A check is made todetermine if it is time to display the contents of the megawatthourtally on the display. If so, this quantity is formatted into four digitvalues and stored in the digit value locations in RAM corresponding tothe numeric display 82.

Line 3 of port 2 is now activated to select multiplexer 166 and deselectmultiplexer 168 as an input to multiplexer 158. An analog to digitalconversion is now made on the panel switches 102, 104, and 106, and adigital value unique to each combination of switch settings stored inRAM.

FUNCT4--FIG. 21

The first task of FUNCT4 is to call the common display routine to lightDIGIT4, the fourth digit from the right on the numeric display indicator82, and read the PF×LV potentiometer 110 and return a digital valuetherefrom. The READ routine is now called to obtain the look-up tablevalue corresponding to the digital value of the PF×LV potentiometer 110.If it is time to display the PF×LV value, it is formatted into fourdigit values and stored in the RAM locations corresponding to numericdisplay indicator 80.

Line 3 of port 2 now selects multiplexer 166 as input throughmultiplexer 158 to the ADC 156, and an analog to digital conversion isordered on the voltage divider network which includes the pushbuttonswitches 105, 107, 128, and 130. A unique digital value corresponding tothe pattern of pushbuttons now depressed is stored in RAM. This quantityis also checked to determine if any pushbuttons have indeed beenpressed. If none, then FUNCT5 is entered. Otherwise, a check is made todetermine if the kilowatt reset pushbutton 105 has been pressed. If so,the value of peak kilowatts in RAM is cleared. Next, a check is made todetermine if the system reset pushbutton 107 has been pressed. If so,all trip indicators are cleared, the serial output pulse codes arezeroed, the display sequence is reset, and the interrupt is enabled. Ifthe system reset button is not being pressed, then one of the testpushbuttons 128 and 130 is. The digital value of the pushbutton readthrough the multiplexers 166 and 158 is now stored in a test flag.

FUNCT5--FIG. 22

The common display routine is called to light DIGIT5, the fifth digitfrom the right, and to read the instantaneous current pick-uppotentiometer 112. The READ routine takes the digital value of thepotentiometer setting supplied by the common display routine and obtainsthe actual setting from the look-up table in ROM. A check is now made todetermine if it is time to display the instantaneous current pick-upsetting on the numeric indicator 80. If so, the instantaneous pick-upvalue is formatted into four digit values and stored in RAM locationscorresponding to the digits of the numeric indicator 80.

The TEST potentiometer 120 is now read through the multiplexers 168 and158 and a digital value obtained. The digital value previously obtainedfrom scanning the front panel switches is now checked to determine ifthe switch 106 is in the TRIP position. If so, a fixed value is loadedinto the RAM location where the value of the TEST potentiometer 120would normally be stored. This fixed value is interpreted as either 6.0per unit for phase current or 1.5 per unit for ground current, at alater point in the execution of the test. If the switch 106 is in the NOTRIP position, a check is next made to determine if more than onepushbutton is pressed. This is an illegal condition, and no test will beperformed. If it is determined that only one pushbutton is pressed, acheck is made to see which one it is. If the GROUND TEST pushbutton 130is pressed, a check is made to determine if the value of the TESTpotentiometer 120 as stored in RAM is greater than or equal to thepresent value of ground current. If it is not, this means that theactual value of ground current now being detected by the system isgreater than the value of ground current simulated by the potentiometer120. Thus, no test will be performed and the trip unit will execute thestandard ground current limit checks. If the value of the TESTpotentiometer 120 as stored in RAM is greater than the present value ofground current, then indexes are set to turn on the TEST LED 100, thevalue of the TEST potentiometer 120 is formatted into four digit valuesand stored in the RAM locations corresponding to the digits of thenumeric indicator 82, and the display of the numeric indicator 82frozen.

If the PHASE TEST pushbutton 128 is pressed, a check is made todetermine if the value of the TEST potentiometer 120 as stored in RAM isgreater than the present phase current. If it is not, then the actualvalue of phase current is more critical than the simulated test value,and no test will be performed. Instead, the normal limit checks on thepresent phase current will be executed by the system. If the simulatedtest value of phase current is greater than the present value of phasecurrent, then an index is set to turn on the TEST LED 100, the value ofthe TEST potentiometer 120 is formatted into four digit values andstored in RAM locations corresponding to the digits of the numericindicator 80, and an index set to freeze the numeric indicator 80.

A check is now made to determine if the test flag is equal to the bitpattern produced by scanning the pushbuttons. If it is, this indicatesthat the TEST pushbutton is still being depressed. Since a test is notto be initiated until the button is released, no test will be performedat this time. If the test flag value is different from the pushbuttonvalue, a check is made to determine if the PHASE TEST pushbutton 128 hadbeen pressed. If so, the value of the TEST potentiometer 120 is storedin the RAM locations corresponding to present phase current and longdelay phase current. If the GROUND TEST button had been pressed, thenthe value of the TEST potentiometer 120 is stored in the RAM locationcorresponding to the present ground current value. This completes theportion of the testing function incorporated in function 5.

Next, the present value of phase current is compared to theinstantaneous current pick-up as specified by the potentiometer 112. Ifthe present value of phase current is below this value, then function 6is immediately entered. If the present value of phase current is greaterthan the instantaneous current pick-up level, an index is set to causethe common display subroutine to put out a pattern of pulses on theserial output terminal to indicate that an instantaneous trip hasoccurred and the TRIP subroutine is called, as will be explained in alater section.

FUNCT6--FIG. 23

The common display routine is executed to light DIGIT6, and read andconvert the long delay pick-up potentiometer 114. The digital value ofthis potentiometer is now acted upon by the READ routine to obtain thetable look-up value. If it is time to display the long delay pick-upvalue on the numeric indicators, the long delay pick up value isformatted into four digit values and stored in the RAM locationscorresponding to the digits of the numeric indicator 80. Next, the longdelay time potentiometer 122 is scanned and converted to a digitalvalue, and acted on by the READ routine to obtain the table look-upvalue for the long delay time function.

The long delay limit check is now made, by first comparing the longdelay phase current to the long delay pick-up value. If the long delayphase current is not greater than the long delay pick-up, then the longdelay tally is reduced by the square of the difference between the longdelay pick-up setting and the long delay phase current. FUNCT7 is thenentered.

If the long delay phase current is greater than the long delay pick-upvalue, then the long delay tally is incremented by the square of thelong delay phase current. A check is now made to determine if the longdelay tally is greater than the value of long delay tally specified fora long delay trip. If not, FUNCT7 is then entered. If the current valueof the tally is greater than the trip level, a code is stored in RAM tocause the common display program to generate the proper pulse code overthe serial output terminal to indicate a long delay trip. Next, the TRIPsubroutine is called, and the long delay tally cleared. FUNCT7 is thenentered.

FUNCT7--FIG. 24

The common display program is called to light DIGIT7 and obtain adigital value for the setting of the short delay pick-up potentiometer116. The READ routine is then called to obtain the proper table look-upvalue for short delay pick-up corresponding to the digital value scannedfrom the potentiometer. A check is made to determine if it is time todisplay the short delay pick-up function. If so, the short delay pick-upvalue is formatted into four digit values and stored in the RAMlocations corresponding to the digits of numeric display indicator 80.

Line 3 of port 2 is now activated to select multiplexer 166, scan theshort delay time potentiometer 124, and obtain a digital valuetherefrom. The table look-up value for short delay time is then obtainedthrough the READ routine. If it is now time to display the short delaytime value, the short delay time value is formatted into four digitvalues and stored in the RAM locations for display as digits 1 through 4in numeric display 82.

The short delay limit value check is now performed, by first comparingthe present phase current to the short delay pick-up setting. If thepick-up setting is not exceeded, then the short delay tally is clearedand FUNCT8 entered.

If the present phase current is greater than the short delay pick-upvalue, the RAM location corresponding to the pattern of switches 102,104 and 106 is checked to determine if the short delay I² T function iscalled for, via the switch 102. If so, the square of the present phasecurrent is added to the short delay tally, and the new value of theshort delay tally compared to the short delay tally trip level. If thetrip level is exceeded, pulse code for serial out and remote indicatoris stored and the TRIP subroutine is called. If the tally trip level isnot exceeded, then FUNCT8 is entered.

If the I² T function was not specified for the short delay test, thenthe present phase current value is added to the short delay tally and acomparison made to determine if the new value of the short delay tallynow exceeds the short delay tally trip level. If not, FUNCT8 isimmediately entered. If the tally trip level is exceeded, the pulse codefor serial out and remote indicators is stored and TRIP routine iscalled before entering FUNCT8.

FUNCT8--FIG. 25

The common display routine is called to light DIGIT8, the leftmost digitin numeric display indicator 80 and to scan and convert the ground faultpick-up potentiometer 118. The look-up table value for ground faultpick-up corresponding to the digital value of the potentiometer 118 isthen determined by the READ routine and stored in RAM. If it is now timeto display the ground fault pick-up value, this quantity is formattedinto four digit values and stored in the RAM locations corresponding tothe four digits of the numeric indicator 80.

The ground fault time potentiometer 126 is now scanned and a digitalvalue obtained therefor. The READ routine then determines the look-uptable value corresponding to the digital value for the potentiometer126. If it is time to display the ground fault time value, this quantityis formatted into four digit values and stored in the RAM locationscorresponding to the four digits of the numeric indicator 82.

A test is now made to determine if the present value of ground faultcurrent is greater than the ground fault pick-up level. If not, anadditional test is made to determine if the present value of groundfault current is greater than one-half of the ground fault pick-uplevel. If so, the ground fault interlock flag is set in RAM. The groundfault tally is then decremented and the loop returns to FUNCT1.

If the present value of ground fault current is greater than the groundfault pick-up level, the location in RAM specifying the front panelswitch pattern is then checked. If the ground fault I² T switch 104 isset, a quantity equal to 1.5 times the present value of ground faultcurrent is added to the ground fault tally. If the I² T switch 104 isnot set, then the ground fault tally is merely incremented.

Next, a check is made to determine if the ground fault tally is greaterthan the ground fault time limit value. If not, the main loop is enteredonce again at FUNCT1. If the tally is greater than the ground faulttime, then a pulse code is stored to allow the proper pulse pattern tobe transmitted on the serial output terminal, and the TRIP routine iscalled prior to returning to the top of the main loop at FUNCT1.

TRIP--FIG. 27

This subroutine is executed whenever electrical conditions on thecircuit breaker exceed the time-current characteristic limit values asentered through the front panel of the trip unit 26. The out-of-limitconditions are detected by the calling functions of the main loopinstructions stored in the ROM.

The TRIP subroutine first checks the trip flag to determine if this tripcondition was detected on a previous execution of the main loop. If so,the next step is to set register R7 to freeze the numeric display. Ifthis is the first time the trip condition has been detected, then thetrip flag is reset and the present value of phase current is loaded intothe digit value locations in RAM corresponding to the digits of numericdisplay 80. Next, bit 6 of the appropriate digit value location in RAMis set, to cause the proper LED to be lighted on the front panel todisplay that function which caused the trip operation. Note that whenbit 6 of a digit value is sent out on port 2, line 6 of port 2 will beactuated when and only when the digit connected to the proper LED islighted. This will turn on the transistor 208, lighting the proper LED.

Register R7 is then set to freeze the numeric display and prevent any ofthe functions of the main loop from attempting to display a differentquantity. The interrupt is now disabled and a check is made to determineif this call to the TRIP routine was the result of a test beingperformed; that is, as a result of the operator having pressed eitherthe PHASE TEST button 128 or the GROUND TEST button 130. If so, a checkis next made to determine if the switch 106 is in the NO TRIP position.If so, the routine resets the test flag and four second timer andreturns to the calling location.

If the switch 106 is in the TRIP position, or if the call to the TRIPsubroutine was not caused by a test, then line 4 of port 1 is actuated.This sends a signal over the line 190 of FIG. 2 to the transistor 192,actuating the trip coil 22 and causing the contacts 18 to open. The testflag and four second timer are reset and the subroutine returns to thecalling location.

READ--FIG. 28

This subroutine performs a table look-up function to allow the limitvalue setting potentiometers on the front panel of the trip unit 26 toselect any of eight discrete values rather than a continuously variableoutput. In addition, the subroutine provides a hysteresis effect whenadjusting the potentiometers to eliminate the undesirable variation ofpotentiometer values on ambient temperature and provide greater ease andconvenience in adjustment.

Upon entry to the READ routine, register R0 contains the address in RAMof the location where the parameter value being read will be stored,register R2 contains the beginning address of the table of eight valueswhich can be selected by the potentiometer, and the accumulator andregister R3 both contain the digital value of the voltage settingproduced by the potentiometer, as supplied by the ADC 156.

A check is first made to determine if a tripping operation has alreadyoccurred. If so, the subroutine is immediately exited. Otherwise, theeight-bit digital value of the potentiometer voltage setting has itslower five bits stripped off and the three most significant digitsrotated to become the least significant bits. The accumulator thuscontains a binary number having a decimal value from 0 to 7. Thisquantity is then added to the address of the beginning of the table, asstored in register R2, yielding the address in RAM of the table valueselected by this particular adjustment of the potentiometer. The valuethus obtained may or may not be used to update the specific parameterbeing adjusted, depending on the previous value of this potentiometer.If the old setting is equal to zero, then a start-up condition exists.The new setting is immediately loaded into the appropriate RAM locationand the subroutine READ is exited.

If the new setting as obtained from the lookup table is equal to the oldsetting, then the old setting is reloaded into RAM at the addressspecified by register R0. If the new setting is unequal to the oldsetting then the hysteresis test is performed.

Essentially, the hysteresis test examines the entire eight-bit output ofthe ADC 156, as scanned from the potentiometer. If bits 1 and 2 areequal, that is, if they are either 00 or 11, then the new setting isignored and the old setting is reloaded into RAM. The purpose of thisaction can be understood by reference to TABLE I, wherein eight valuesout of the 128 possible combinations of ADC output are shown. As hasalready been explained, the most significant bits, that is bits 5, 6 and7, determine the setpoint of the potentiometer. As can be seen in TABLEI, the potentiometer setting in binary notation will increase from 100to 101 as the analog-to-digital converter output moves from value D tovalue E. By ignoring a change in potentiometer setting wherein bits 1and 2 are either 11 or 00, a hysteresis effect is obtained.

                  TABLE I                                                         ______________________________________                                        Bit                                                                           Number: 7     6     5   4   3   2   1   0                                     ______________________________________                                                                                         Value                                                                         .                                                                             .                                                                             .                            1         0     0     1   1   1   0   0                                                 A                                                                   1         0     0     1   1   1   0   1                                                 B                                                                   1         0     0     1   1   1   1   0                                                 C                                                                   1         0     0     1   1   1   1   1                                                 D                                                                   1         0     1     0   0   0   0   0                                                 E                                                                   1         0     1     0   0   0   0   1                                                 F                                                                   1         0     1     0   0   0   1   0                                                 G                                                                   1         0     1     0   0   0   1   1                                                 H                                                                   ______________________________________                                    

Remembering that the hysteresis test is only performed if there is achange in the upper three bits of the ADC output, it can be seen that anincrease in ADC output from value B to value C will not result in a newvalue being stored, since the upper three bits of B and C are the same.An increase from value B to value G, however, would clearly result in anew value being stored, since bit 5 of the output changed from a zero toa one.

Without the hysteresis test being performed, an increase in ADC outputfrom value C to value F would similarly result in a new potentiometervalue being stored. However, this represents a change in value of about3/256 of the maximum potentiometer, or less than 1.2%. Such variationcan easily occur due to changes in ambient temperature.

Through the use of the hysteresis test, wherein ADC outputs having equalvalues of bits 1 and 2 are ignored, it can be seen that a change in ADCoutput from value C to value F would result in the new potentiometersetting being ignored and the old potentiometer setting being reloadedinto RAM, since bits 1 and 2 of value F are both zero. Similarly, if theoperator were reducing the value of the potentiometer, causing an ADCoutput to change from value G to value C the new value would also beignored and the old value retained, since bits 1 and 2 of value C areboth one, and the hysteresis test would reject the new setting. It cantherefore be seen that the hysteresis test insures that thepotentiometer setting must be changed by more than 4/256 of its totalpossible adjustment before a new setting will be accepted. It can beargued that the hysteresis test just described is not sufficientlyprecise, in that a valid setting change may possibly be ignored. Thismight occur, for example, if the old potentiometer setting produced anADC output much larger than value H, for example 10110101, and the newpotentiometer setting produced an ADC output equal to value D. It can beseen that this represents a very large excursion in the rotation of thepotentiometer, and yet the final position producing a value equal tovalue D would be ignored, since bits 1 and 2 are both ONE's. It must beremembered, however, that an interactive operation is being performed,and that the parameter value selected by the READ routine is, from thepoint of view of a human operator, instantaneously presented on thenumeric displays 80 or 82. In the example just cited, the operator wouldsee that a fairly large excursion of the potentiometer produced nochange in value, and he would naturally make an even further adjustment.At some point, his further adjustments would result in a new value beingselected by the READ routine and presented under numeric display. If thechange produced were larger than desired, the operator would thenreadjust in the opposite direction, the entire operation taking muchless time to perform than to explain. This represents an extremelycost-effective and convenient method of entering parameter changes forthe time current tripping characteristic into a circuit breaker.Adjustment of the potentiometer to the extreme upper and lower limitswill cause the most conservative value to be displayed.

In the event that bit 2 is not equal to bit 3, that is the hysteresistest does not cause the setting to be ignored, a bit pattern is loadedin register R7 to cause display of this setting value on the numericdisplays 80 or 82. The four-second timer is then reset and the newsetting value is stored in the RAM location corresponding to thisparticular parameter. The subroutine then returns to the callingfunction.

If an ADC output of all zero's or all one's is obtained, the READroutine interprets this as a potentiometer failure. The mostconservative parameter value is then selected from the look-up table,displayed on the numeric display 80 or 82, and stored in RAM.

I. Hardware Initialization After Power-On FIG. 16

The microcomputer 154 must be initialized following power-up. In thecase of the Intel 8048 device this is accomplished by means of a RS pinwhich if held low causes the program to "jump" to address 0 which byconvention is the starting address of the power-on startup subroutine.The RS pin is held low by the power supply by means of D900 for about 5ms, after the +5 VDC is applied.

However, the RS pin does not affect the I/O lines from the microcomputerand thus during the power ON transient these may assume either a high orlow output state which, in the case of four particular lines of Port 1and Port 2, can cause excessive power supply drain or even accidentaltripping of the circuit breaker 10 or other interconnected breakers.These lines are as follows:

1. LED (line 6 of Port 2--should be low to ensure all LED indicators onfront panel are OFF).

2. INHIBIT 212 (line 7 of Port 2--should be tristated, that is, held ina high-impedance state to ensure that all 8 digits of the 7-segment LEDdisplays 80 and 82 are OFF).

3. PULSE 178 (line 7 of Port 1--should be tristated to ensure that pulsetransformer 501 is OFF).

4. TRIP 190 (line 4 of Port 1--should be tristated to ensure that nofalse trip occurs on power-on).

The desired tristating is achieved by means of hex buffer U900. When RSof the microcomputer 154 is low, the DISABLE (A) of U900 is low(removed) which causes DISABLE (B) to be high (active). In this way thefour critical leads from the microcomputer 154 are switched to the highimpedance state, except for LED which is held low as desired by thepull-down resistor R905.

A second function of U900 is to reset counter U901 as shown in FIG. 16.

J. Automatic Reset FIG. 16

Once a successful power-up transition is made, the microcomputer 154continues to execute a logical and sequential series of instructionsindefinitely. Under unusual conditions, such as those produced byelectrical system transients, it is possible for an instruction to beimproperly executed. The only way to restore the microcomputer 154 toits orderly program execution is to perform another reset operation. Inunattended applications, this reset must be automatic.

This is accomplished by means of counter U901 which utilizes a 400 kHzclock output (ALE) from the microcomputer 154 to provide a fixed timedelay between the last U901 RS pulse and a high on Q11 (RS for the μC).If the RS pulse of U901 occurs soon enough, Q11 will remain low and theμC will not be reset.

The U901 RS pulses are derived from the collector of transistor 228.Normally these pulses are 100 μs wide and occur approximately every 2ms. The circuit is designed so that 5.46 ms is required for Q11 to timeout (go high) and thus Q11 is always low.

If improper instruction execution sequence occurs, the followingpossible conditions would cause an automatic reset of the microcomputer(Q11 would time out).

228-ON

If this condition should exist for more than 300 μs, pulse transformer501 will saturate and U901 RS will remain low.

228-OFF

If this condition should exist, U901 RS will remain low.

228-Pulse Rate Too Slowly

If transistor 228 turn-on pulses occur less than every 5.46 ms, the U901RS will be low long enough for a μC reset to occur.

228-Pulsed Too Fast

Rapid pulsing of transistor 228 will be filtered by R900 and C900 (39 μstime constant).

228-ON/OFF Duty Cycle>1/10

Transformer T501 is pulsed on for 100 μs, to a voltage of 5 volts, bytransistor 228. When 228 is turned OFF, the transformer's magnetizingcurrent will flow through diode D901 which will result in a voltage ofabout -0.5 volts being applied to the transformer 501. The averagevoltage of the transformer must be zero and thus 1000 μs ##EQU1## willbe required to "reset" the transformer's magnetizing current to zero. A1-to-10 or less ON-to-OFF ratio must be maintained for the transformer501 to function or the transformer's core will ultimately saturate. Iftransformer 501 is saturated, the RS pulses will not be applied to U901and Q11 will time out and reset the microcomputer.

What we claim is:
 1. Circuit interrupter apparatuscomprising:interrupter means for conducting current flow through anassociated circuit and for operating to interrupt current flowtherethrough upon command; a phase current transformer coupled to theassociated circuit; trip unit means connected to said phase currenttransformer for comparing the output of said phase current transformerto a predetermined time-current trip characteristic and for operatingsaid interrupter means whenever said output exceeds limits defined bysaid time-current trip characteristic;and power supply means connectedto said phase current transformer and to a source of external power forsupplying operating power to said trip unit, said power supply meansselecting the most appropriate power source as between said phasecurrent transformer and said external power source.
 2. Apparatus asclaimed in claim 1 comprising a ground current transformer coupled tothe associated circuit and connected to said power supply, and saidpower supply means comprises means for selecting either said phasecurrent transformer output or said ground current transformer output forcomparison against an external power source, according to which of saidcurrent transformers has the highest output current.
 3. Apparatus asrecited in claim 1 comprising means adapted for connection to aplurality of external power sources, and means for selecting the one ofsaid external power sources having the highest current output. 4.Circuit interrupter apparatus, comprising:interrupter means forconducting current flow through an associated circuit and for operatingto interrupt current flow therethrough on command; sensing means forsensing current flow through said interrupter means; trip unit meansconnected to said interrupter means and said sensing means for operatingsaid interrupter means whenever current flow therethrough exceeds apredetermined time-current trip characteristic, said trip unit meanscomprising electronic circuit means for providing a plurality offunctions; and power supply means connected to said sensing means forsupplying operating power to said trip unit means, said trip unit meanscomprising low-power condition sensing means for causing said electroniccircuit means to execute a subset of said plurality of functions upondetection of low-power conditions at the input of said power supplymeans.
 5. Apparatus as recited in claim 4 wherein said power supplymeans produces pulses of operating power to said trip unit means upondetection of low-current conditions.
 6. Apparatus as claimed in claim 5wherein said trip unit means comprises a numeric display device andmicrocomputer means for causing said display device to display aplurality of sequential numeric values under normal conditions and forexecuting a plurality of protection functions during a predeterminedtime period less than the duration of said power pulses, saidmicrocomputer means comprising means for altering said normal displaysequence, for executing all of said protection functions, and fordisplaying a predetermined one of said normal display values during suchlow-power conditions as would cause generation of said operating powerpulses.
 7. A circuit breaker, comprising:interrupter means comprising aspring-powered mechanism for conducting current flow through anassociated circuit and for operating upon energization for apredetermined time period to interrupt the current flow therethrough oncommand; sensing means for sensing current flow through said interruptermeans; trip unit means connected between said interrupter means and saidsensing means for comparing current flow through said interrupter meansto a predetermined time-current trip characteristic and for operatingsaid interrupter means whenever current flow therethrough exceeds saidtime-current trip characteristic; power supply means for supplying allelectrical operating power to said trip unit means and to saidinterrupter means;and a non-latching switching device for energizingsaid interrupter means from said power supply means upon actuation bysaid trip unit means; said trip unit means actuating said non-latchingswitching device for said predetermined time period, whereby saidinterrupter means operates to interrupt current flow on the associatedcircuit whenever current flow therethrough exceeds a time-current tripcharacteristic, but does not so operate when said non-latching switchingdevice is actuated by noise pulses less than said predetermined timeperiod.
 8. Apparatus as claimed in claim 7 wherein said power supplymeans comprises an energy storage device.
 9. Apparatus as claimed inclaim 8 wherein said energy storage device comprises a battery. 10.Circuit interrupter apparatus, comprising:interrupter means forconducting current flow through an associated circuit and for operatingto interrupt current flow therethrough on command; sensing means forsensing current flow through said interrupter means; trip unit meansconnected to said interrupter means and said sensing means for comparingcurrent flow through said interrupter means to a predeterminedtime-current trip characteristic and for operating said interruptermeans whenever current flow therethrough exceeds said time-current tripcharacteristic; and power supply means connected to said sensing meansfor supplying operating power at a first voltage to said trip unit meansand operating power at a second voltage to said interrupter means; saidtrip unit means comprising means for detecting impending failure of saidpower supply means to supply adequate operating power to said trip unitmeans and to said interrupter means and for executing a predeterminedpower-down protection sequence to prevent nuisance tripping upon failureof said operating power.
 11. Apparatus as recited in claim 10 whereinsaid power supply means comprises energy storage means for storing anamount of energy sufficient to maintain operating power to said tripunit means and said interrupter means for a predetermined time, and saidpower supply means comprises time delay means for maintaining operatingpower to said trip unit means from said energy storage means for apredetermined time sufficient to execute a power-down sequence andprevent nuisance tripping upon failure of operating power to said tripunit means.
 12. Apparatus as recited in claim 11 wherein said powersupply means comprises means adapted for drawing supply power from aplurality of power sources, and said power supply means comprises a likenumber of criteria for determining failure of said power sources. 13.Circuit interrupter apparatus, comprising:interrupter means forconducting current flow through an associated circuit and for operatingto interrupt current flow therethrough on command; sensing andempowering means for sensing current flow through said interrupter andfor supplying operating power to said interrupter means and toassociated electronic circuitry; trip unit means connected to saidinterrupter means and to said sensing and empowering means for comparingcurrent flow through said interrupter means to a predeterminedtime-current trip characteristic and for operating said interruptermeans when current flow therethrough exceeds time-current tripcharacteristics; and power supply means connected to said sensing andempowering means, to said trip unit means, and to said interrupter meansfor supplying operating power from said sensing and empowering means tosaid trip unit means and to said interrupter means, said power supplymeans comprising energy storage means and shorting means for divertingthe output of said sensing and empowering means from said energy storagemeans and for supplying a short circuit across the output of saidsensing and empowering means when said sensing and empowering meansoutput rises above a predetermined level.
 14. Circuit interrupterapparatus, comprising:interrupter means for conducting current flowthrough an associated circuit and for operating to interrupt currentflow therethrough on command; a current transformer for providing thedual function of sensing current flow through said interrupter means andderiving power from the associated circuit; trip unit means connected tosaid interrupter means and said current transformer for operating saidinterrupter means whenever current flow therethrough exceeds apredetermined time-current trip characteristic; and power supply meansconnected to said current transformer for supplying operating power tosaid trip unit means, said trip unit means comprising means for sensinglow-power conditions at the input of said power supply means; said powersupply means comprising means producing pulses of operating power tosaid trip unit means upon detection of low-current conditions.